Sulfide coating



pends somewhat on the particular acid chosen, the concentration of the added anion, the degree of pickling action produced, the particular steel being coated and the degree of pickling which can be tolerated for the type of coating desired. However, it may be stated as a general rule that the pH range to be used is from 0.3 to 1.1. No particular advantage is gained by operating at the extreme limits of acid concentration since the entire advantage of the invention can be obtained when the pI-I is less than 1.1 and substantially above 0.5. If, however, it be desired to operate at the lowest possible pH, it is a matter of a few simple tests to establish the lower limit permissible With the particular steel and the particular anion which it is desired to use.

'I'he sulte ion concentration is normally maintained at about 0.3 to 1.3% but this proportion has been varied over relatively Wide limits. Itis preferred that the chloride ion or equivalent anion be maintained above about 1% in order to secure the maximum benefits from the invention, but some advantage can be gained with very minor percentages. Highly concentrated solutions, up to saturation, of the various anions can be used but little advantage is gained above 1.3% sulte or about 5% of the activating anion.

Since hydrochloric acid is a source of both acid and chloride ion it may be the sole added agent, its minimum concentration being determined by the pI-I of the solution. Similarly, and where a small percentage of chloride ion is desired, hydrochloric acid may be used as a source of chloride ion and a second acid may be added to adjust the solution to the acidity desired. The proportion of hydrochloric acid required to produce a pH below 1.1 will provide a chloride percentage in excess of about 0.4%. Thus, for example, a solution containing less than about 0.4% can be made by using a limited proportion of hydrochloric acid and acidifying the solution to a pH below 1.1 with a second acid.

The particular acid selected is not important except that it be strong enough to provide the required pI-I. The mineral acids `are both stronger and inexpensive as compared with other acids, e. g., benzene sulfonic and trichloracetic, and hence are preferred. Sulfuric, hydrochloric, and nitric acids are especially preferred. Acids, which are not suiiiciently strong to give the desired pH may be used if a suitable proportion of a stronger acid is used in the same composition. Similarly the source of sulte, chloride, etc., is not important provided the cation provided with said anion be compatible with the solution; that is, not precipitate out an essential ingredient or have any other adverse elfect on the solution or the coating.

The metals treated comprise the entire category of steels including mild steels, corrosion resistant, and stainless steels and, as pointed out previously, the invention has particular advantage in treating stainless steels because of the avoidance of the high temperatures normally required in their coating. The coatings produced are salts of the metals treated and vary somewhat with different alloys. Certain of the metals encountered in alloy steels have a tendency to form an oxide rather than a sulde and, therefore, the average coating contains some oxide. Nickel appears to be particularly active toward the compositions of the invention 4 and nickel steels usually produce a high percentage of nickel sulfide in the coating.

'Ihe following examples illustrate the borderline conditions where the anion is deficient (Example 1); the acid is deficient (Example 2); and the acid and anion are both sufficient but at a relatively low concentration (Example 3). Example 4 illustrates the effects of increasing percentages of chloride ion on the lowering of the temperature required to obtain a satisfactory coating in three minutes. Three minutes has been chosen as a standard of comparison in the various examples. An 18-8 stainless steel was used in each example to give comparative results.

Eample 1 A solution was made up containing 10- grams of sodium sulte per gallon of water and containing 20 cc. of 95% sulfuric acid. The solution had a pH of 1.1. A temperature of 200 F. was required to produce a coating on the stainless steel in three minutes.

Example 2 A solution similar to that of Example 1 was prepared except that 20 cc. of 36% hydrochloric acid solution was used in place of the sulfuric acid. This produced a solution with a pI-I of 1.5 and a chloride content of 0.2%. Fifteen minutes were required at 200 F. to produce a coating on the stainless steel.

Example 3 The proportion of acid in Example 2 was doubled. This produced a solution with a pH of 1.1 and a chloride content of 0.4%. A good. coating was produced in three minutes at F.

Example 4 A series of solutions containing 5% nitric acid and 0.32% sulte as sodium sullte was made up. Each of the solutions contained successively the following chloride percentages: 0.0, 0.1, 0.2, 0.3, 0.5, and 5.0%. In the solution containing no chloride a coating was produced in 3 minutes at 172 F. and no coating could be produced at 170 F. In the remaining solutions containing from 0.1 to 5% chloride a satisfactory coating was obtained in three minutes at 150, 146, 142, and 100 F. respectively.

Although I do not wish to be limited by theory, I believe that the chloride ion, or equivalent anion, has an activating inuence on the acid attack on the metal. This permits a suitable and controlled attack at a lower temperature for the purpose of forming a coating on the metal. It appears also that the activation does not significantly increase the pickling effect, but, in some cases, may reduce this effect when full advantage is taken of the lowered coating temperature. As indicated previously, the invention permits of a more rapid coating of stainless and corrosion resistant steels and is particularly advantageous in this respect.

I claim:

1. A composition for forming a sulfide coating on a steel surface which consists of an aqueous solution of a member rof the group consisting of the sulfide ion and ions which form the sulde ion through reduction on the steel surface and in a proportion equivalent to about 0.3-1.3 percent suliite ion; a member of the group of anions consisting of chloride, bromide, and iodide, in a proportion of from equivalent to .1% of 'the chloride ion up to and including saturation; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion sufficient to provide a pH in the range of about 0.3-1.1.

2. A composition for forming a sulfide coating on a steel surface which consists of an aqueous solution of a memberl of the group consisting of the sulfide ion and ions which form the sulde ion through reduction on the steel surface and in a proportion equivalent to about 0.3-1.3 per cent sulfite ion; the chloride ion in a proportion lof from .1% up to and including saturation; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion sufficient to provide a pH in the range of about 0.3-1.1.

3. A composition for forming a sulde coating on a steel surface which consists of an aqueous solution of a member of the group consisting of the sulfide ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about 0.31.3 percent sulte ion; the chloride ion in a proportion of from about 1% to about 5%; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion suiiicient `to provide a pH in the range of about 0.3-1.1.

4. The method of forming a sulde coating on a steel surface which comprises contacting the surface with an aqueous solution consisting of water, the sulfide ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about 0.3-1.3 percent sulfite ion; a member of the group of anions consisting of chloride bromide, and iodide, in a proportion of from equivalent to .1 of the chloride ion up to and including saturation; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion sufficient to provide a pH in the range of about 0.3-1.1.

5. The method of forming a sulfide coating on a steel surface which comprises contacting the surface with an aqueous solution consisting of water, the sulde ion and ions which form the sulde ion through reduction on the steel surface and in a proportion equivalent to about 0.3-1.3 percent sulte ion; the chloride ion in a proportion of from .1% up to and including saturation; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion sufficient to provide a pH in the range :of about 0.3-1.1.

6. The method of forming a sulde coating on a steel surface which comprises contacting the surface with an aqueous solution consisting of Water, the sulfide ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about 0.3-l.3 percent sulte ion; the chloride ion in a proportion of about 1% to about 5%; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion sufiicient to provide a pH in the range of about 0.3-1.1.

7. A composition for forming a sulfide coating on a steel surface which consists of an aqueous solution of a member of the group consisting of the sulde ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about 0.3-1.3% sulte ion; a member of the group of anions consisting of chloride, bromide, and iodide in a proportion of about 1% to about 5%; and an acid selected from the group consisting of sulfuric, hydrochloric, and nitric in a proportion sufficient to provide a. pH in the range of about 0.31.1.

8. The method of forming a sulfide coating on a steel surface which comprises contacting the surface with an aqueous solution consisting of water, the suliide ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about 0.3-1.3 sulte ion; a member of the group of anions consisting of chloride, bromide, and iodide in a proportion of about 1% to about 5%; and an acid selected from the group consisting of sulfuric, hydrochloric and nitric in a proportion sufcient to provide a pH in the range of about 0.3-1.1.

9. A composition for forming a sulfide coating on a stainless steel surface which consists of an aqueous solution of a member of the group consisting of the sulfide ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about .3 to 1.3% sulfite ion, the bromide ion in a proportion of from equivalent to ,1% of the chloride ion up to and including saturation, and an acid selected from the group consisting of sulfuric, hydrochloric and nitric in a proportion sufficient to provide. a pH in the range of about .3 to 1.1.

. 10. A composition for forming a sulfide coating on a stainless steel surface Which consists of an aqueous solution of a member of the group consisting of the sulfide ion and ions which form the sulfide ion through reduction on the steel surface and in a proportion equivalent to about .3 to 1.3% sulte ion, the iodide ion in a proportion of from equivalent to .1 of the chloride ion up to and including saturation, and an acid selected from the group consisting of sulfuric, hydrochloric and nitric in a proportion sufficient to provide a pH in the range of about .3 to 1.1.

11. The method of forming a sulfide coating on a steel surface which comprises contacting the surface with a solution consisting of Water, the sulfide ion and ions which form the sulfide ion through reduction on the steel surface, and in a proportion equivalent to about .3 to 1.3% sulte ion, the bromide ion in a proportion of from equivalent to .1% of the chloride ion up to and including saturation, and an acid selected from the group consisting of sulfuric, hydrochloric and nitric in a proportion suicient to provide a pH in the range of about .3 to 1.1.

12. The method of forming a sulde coating on a steel surface which comprises contacting the surface with a solution consisting of water, the sulfide ion and ions which form the sulfide ion through reduction on the steel surface, and in a proportion equivalent to about .3 to 1.3% sulte ion, the iodide ion in a proportion of from .1% up to and including saturation, and an acid selected from the group consisting of sulfuric, hydrochloric and nitric in a proportion sulcient to provide a lpH in the range of about .3 to 1.1.

JOI-IN EDGAR BAXTER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,273,234 Tanner Feb. 17, 1942 2,301,983 Tanner Nov. 17, 1942 2,302,643 Thompson Nov. 17, 1942 2,314,565 'I'hompson Mar. 23, 1943 2,550,660 Amundsen et al May 1, 1951 2,577,887 Gibson Dec. 11, 1951 FOREIGN PATENTS Number Country Date 131,106 Austria Jan. 10, 1933 

7. A COMPOSITION FOR FORMING A SULFIDE COATING ON A STEEL SURFACE WHICH CONSISTS OF AN AQUEOUS SOLUTION OF A MEMBER OF THE GROUP CONSISTING OF THE SULFIDE ION AND IONS WHICH FORM THE SULFIDE ION THROUGH REDUCTION ON THE STEEL SURFACE AND IN A PROPORTION EQUIVALENT TO ABOUT 0.3-1.3% SULFITE ION; A MEMBER OF THE GROUP OF ANIONS CONSISTING OF CHLORIDE, BROMIDE, AND IODIDE IN A PROPORTION OF ABOUT 1% TO ABOUT 5%; AND AN ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC, HYDRO- 